1. Technical Field of the Invention
The present invention relates to a torque limiting apparatus provided in a path of power transmission from a drive source to a drive shaft for vehicles such as trucks.
2. Prior Art
For power transmission from a drive source to a drive shaft for vehicles such as trucks, a conventional structure of gearing system generally used is described with an example of a front-wheel drive vehicle. This well known structure of gearing system is arranged along the longitudinal direction of the vehicle, and so configured that the rear end of the drive shaft is connected to the drive source, and the front end thereof is connected to a differential gear system. A connection between the drive shaft and the differential gear system has been performed by the direct engagement of an output gear mounted at the front end of the drive shaft nonrotatably relative thereto, with the input gear of the differential gear system.
Such a well known structure of gearing system is simple, but there are following disadvantages due to the direct engagement of the drive shaft and the input gear of the differential gear system.
It is desirable that parts configuring vehicles are each made compact for a reduction in cost of vehicles and an improvement in steerability of driving vehicles. On the other hand, it is required for each part to be strong enough to bear a required load. Thus, each part for vehicles are sized as small as possible when a required strength is satisfied for each part. For example, assuming that the dimension of a connection part between the drive shaft and differential gear system is determined, based on a load imposed on said connection portion (hereafter, referred to as a load on a normal driving state) when driving on a terrain with a relatively flat surface. In this case, assuming that drive wheels had an impact load momentary caused by a sudden start or stop of a vehicle, a sudden load (hereafter, referred as a peak load) in excess of the load on a normal driving state, would be imposed on the connection part, thereby the part could be damaged. Consequently, for the well known structure of gearing system, it is required for the connection part between the drive shaft and the input gear of the differential gear system to be large enough to bear the peak load, so the requirement for making a reduction in size can not be sufficiently satisfied.
On the other hand, U.S. Pat. No. 2,977,779 discloses a structure of gearing system in which, as shown in FIG. 4, the front end of a drive shaft, its rear end being connected to a drive source (not shown), and the rear end of a connecting shaft 120, its front end being connected to an input gear of differential gear system (not shown), are connected to each other via a torque limiting apparatus 100. As shown in the figure, the torque limiting apparatus 100 comprises a middle shaft 101 connected via a universal joint 130 to the front end of the drive shaft nonrotatably relative thereto around its axis, drive friction discs 102 mounted on the middle shaft nonrotatably relative thereto, a cylindrical casing 103, which has a closed front end, surrounding the middle shaft 101 and drive friction discs 102, driven friction discs 104 mounted on the inner periphery of the casing 103 nonrotatably relative thereto and bringing into a frictional contact with the drive friction discs 102, and a biasing member 105 for biasing the drive friction discs 102 and driven friction discs 104 in a manner one side is pressed toward the other. A connection between the connecting shaft 120 and the torque limiting apparatus 100, is made by the rear end of the connecting shaft 120 connected to the front end of the casing 103 nonroratably relative thereto.
The torque limiting apparatus 100, allows a power transmission from the drive friction discs 102 to the driven friction discs 104 by means of a frictional contact on a normal driving state, while, in case of having a peak load as mentioned above, the drive friction discs 102 and the driven friction discs 104 slip to each other, thus the power transmission therebetween is cut off. The use of such torque limiting apparatus 100 allows the strength for the connecting part between the connecting shaft 120 and the input shaft of the differential gear system to be determined in accordance with the load on a normal driving state as mentioned above. Namely, the power transmission from the drive source to the differential gear system is cut off upon peak loads, so there is no need for the connecting part between the connecting shaft and differential gear system to be large sized so as to bear against the peak load. In this manner, the dimension of each part can be determined in accordance with the load on a normal driving state, thereby allowing each component to be downsized.
However, the torque limiting apparatus disclosed in the U.S. Pat. No. 2,977,779 mentioned above, requires a lubricating oil for the frictional discs 102, 104, to be enclosed in advance in the casing 103. In addition, the oil enclosed in the casing 103 is not positively cooled down, so there is another problem in that the heat generated by the frictional discs 102, 104 could cause a deterioration in durability and abrasion resistance.
An object of the present invention, which has been accomplished to overcome the foregoing problems, is to provide a torque limiting apparatus for transmitting power from an output end of a drive shaft, the input end of which is connected to a drive source, to a differential gear system for driving a pair of drive wheel axes, the apparatus being adapted to supply a lubricating oil automatically thereinto.
To fulfill the foregoing object, the present invention provides a torque limiting apparatus for transmitting power from a drive shaft connected to a drive source, to a differential gear system for driving a pair of wheel axes, the apparatus comprising: a connecting shaft, an output side of which is connected to the differential gear system, an input side of which is protruded out of an opening formed at a housing of the differential gear system; a hollow cylindrical casing supported on the input side of the connecting shaft rotatably relative thereto, and connectable to the connecting shaft; a seal member for liquid-tightly connecting the output opening of the casing and the opening of the housing; and a connecting mechanism provided between the casing and the connecting shaft, for transmitting only a partial power less than a predetermined torque value out of whole power input into the casing, to the connecting shaft.
Preferably, the apparatus can be further provided with a mount flange which closes liquid-tightly the input opening of the casing and is connected to the drive shaft.
More preferably, the apparatus can be so constructed that the flange has a center bore formed in communication with both the inside and outside of the casing, the connecting shaft comprising: a supporting shaft, an output end of which is connected to the differential gear system, and an input end of which is protruded liquid-tightly out of the center bore of the flange, a middle shaft supported on the supporting shaft nonrotatably relative thereto and axially movable, an input end of the middle shaft being protruded liquid-tightly out of the center bore of the flange, the connecting mechanism can be provided between the middle shaft and the casing, and a locking member can be provided in the housing for positioning the output end of the middle shaft, and a locking device removably fixed to the input end of the supporting shaft, so that the axial movement of the middle shaft can be prevented in cooperation with the locking member.
Preferably, the connecting mechanism can be so constructed that drive frictional discs provided onto the inner periphery of the casing nonrotatably relative thereto, and driven frictional discs provided onto the outer periphery nonrotatably relative thereto, corresponding to the drive frictional discs, and adapted to be brought into a frictional contact with the drive frictional discs, and a biasing member arranged in the casing so that the drive and driven frictional discs are biased in a manner one side is pressed toward the other at a predetermined bias force.
More preferably, the connecting mechanism can be further provided with a adjustment member for adjusting the bias force of the biasing member.
As explained above, the torque limiting apparatus embodying the invention comprises a connecting shaft, its output side being connected to a differential gear system, its input side being protruded out of an opening formed at a housing of the differential gear system; a hollow cylindrical casing supported on the input side of the connecting shaft rotatably relative thereto, and adapted to be connectable with respect to the connecting shaft; a seal member for liquid-tightly connecting the output opening of the casing and the opening of the housing; and a connecting mechanism provided between the casing and the connecting shaft, for transmitting only a partial power less than a predetermined torque value out of whole power input into the casing, to the connecting shaft, so that a lubricating oil to be supplied to the differential gear system can be automatically supplied to the connecting mechanism through a gap formed between the connecting shaft and the casing. In addition, the oil supplied to the mechanism can be also circulated to the differential gear system through the gap. Consequently, a heat generation caused by the connecting mechanism can be effectively reduced, thereby allowing an improvement in durability and abrasion resistance.
The apparatus can be further provided with a mount flange which closes liquid-tightly the input opening of the casing, and is connected to the drive shaft, so as to prevent a lubricating oil supplied into the connecting mechanism from leaking out.
Further, the apparatus can be so constructed that a center bore is formed at the flange, the connecting shaft is adapted to be a double structure having a supporting shaft connected to the differential gear system, and a middle shaft supported on the supporting shaft nonrotatably relative thereto and axially movable, both input ends of the supporting shaft and middle shaft are protruded liquid-tightly out of the center bore, the connecting mechanism can be provided between the middle shaft and the casing, and the middle shaft is fixed axially nonmovable by a locking member provided in the housing and a locking device removably fixed on the input end of the supporting shaft, so that the casing, the flange, the middle shaft and the connecting mechanism can be all assembled in one unit in advance, thereby after the differential gear system is attached, the assembly unit can be separately incorporated into the apparatus. Thus, typical assembly works for incorporating the connecting mechanism into the casing, made in a limited space, can be eliminated, thereby allowing an improvement in efficiency of assembly works.
Further, the torque limiting apparatus can be so constructed that the connecting mechanism comprises drive frictional discs adapted to be nonrotatably relative to the casing, driven frictional discs adapted to be nonrotatably relative to the drive discs, and a biasing member for biasing the drive and driven discs in a manner one side is pressed toward the other, and that an adjustment member for adjusting a bias force of the biasing member, is further provided, and then an adjustment of the maximum torque value transmitted from the casing to the connecting shaft, can be achieved.
Alternatively, the torque limiting apparatus transmitting power from a drive shaft connected to a drive source, to a differential gear system for driving a pair of wheel axes may comprise:
a connecting shaft, the output side of which is connected to the differential gear system, the input side of which is protruded out of an opening formed at the housing of the differential gear system; a hollow cylindrical casing supported on the input side of the connecting shaft rotatably relative thereto, and a mount flange connected at the input end to the drive shaft; and a connecting mechanism provided between the inner periphery of the casing and the outer periphery the connecting shaft, for transmitting only a partial power less than a predetermined torque value out of whole power input into the casing, to the connecting shaft.
The invention will be further clarified by the description of embodiments with reference to the following accompanying drawings. The invention is not limited to these embodiments, but various modifications are possible without deviation from the scope of the claims.